Process for the production of olefins



Patented .Fune 13, 1939 UNITED STATES PATENT OFFICE PROCESS FOR THEPRODUCTION OF OLEFINS Hans Baehr, Ludwigshafen-on-the-R.hine,' Germany,assignor to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-onthe-Main, Germany 2 Claims.

The present invention relates to the production of olefins bydehydrogenation of saturated hydrocarbons.

It has already been proposed to convert gase- 5 ous or vaporous.(hereinafter referred to as vaporized) saturated hydrocarbons, inparticular those of the parafiin series, such as ethane or propane orthe like, nto olefins by dehydrogenation effected by heat-treatment at atem-- l0 perature of about 700 C. This conversion may be promoted by theaddition of oxygen or gases containing the same or by the presence ofcatalysts such as silica gel or metal oxides. If lower temperatures areemployed the yields of olefins obtained are not very satisfactory, agreat part of the initial hydrocarbons remaining unchanged. At highertemperatures greater yields in olefins are secured, however, in thiscase also side reactions take place by which a considerable part of theinitial hydrocarbons or the oleflns formed is consumed.

I have now found that the conversion of vaporlzed saturated hydrocarbonscontaining more than one carbon atom in the molecule into olefins iseffected with great advantage at temperatures between 400 and 700 C. inthe presence of free elementary sulphur or substances containing sulphurin the free elementary form or substances supplying free elementarysulphur under the conditions of Working, all these substanceshereinafter being referred to as those comprising free elementarysulphur. The sulphur in this treatment combines with two hydrogen atomsof the particular saturated hydrocarbons employed with the formation ofthe olefins having the same number of carbon atoms as the said saturatedhydrocarbons and of hydrogen sulphide. In the case of the conversion ofbutane into butylene the course of the reaction may be illustrated bythe following equation:

considerably increase the surface presented to the reacting gases orvapors, as for example 55 pumice, silica gel, silicon or coke, whichsubstances, if desired, may be activated by other materials promotingthe dehydrogenation, such as antimony, tellurium' or bismuth.Temperatures at which sulphur reacts with hydrocarbons with theformation of carbon disulphide 5 should of course be avoided. Anaddition of a small amount of oxygen or air to the hydrocarbons to beconverted favors the formation of unsaturated hydrocarbons.

As substances containing or supplying sulphur 10 which may be used inthe present process may be mentioned pyrite or the waste materialsemployed for purifying gases containing sulphur, such as waste bog ironore. These substances are preferably heated with the hydrocarbons to 13be converted to such a temperature that the sulphur is freed therefromor that volatile sulphur compounds are formed, the resulting mixture ofhydrocarbons and sulphur or sulphur compounds then being heated to thereaction temperature 20 proper. When employing hydrogen sulphide orother gaseous or vaporous divalent sulphur compounds which do not splitoff free sulphur by the mere action of heating as substances supplyingsulphur, oxygen (which term for the pur- 25 pose of the presentinvention also includes gases containing or supplying oxygen, such asair or sulphur dioxide) is added to the mixture of hydrocarbons andsulphur compounds. In this case the course of the conversion of butanemay 30 be illustrated by the following equations:

By the conversion of hydrocarbons with sulphur hydrogen sulphide isformed in addition to the olefins. This hydrogen sulphide may be madeuse of again for the conversion according to the present invention byadding it to fresh 40 amounts of hydrocarbons to be converted togetherwith a suitable amount of oxygen whereby the hydrogen sulphide isconverted into sulphur which latter then acts upon the saidhydrocarbons. In this manner it is possible to convert large amounts ofhydrocarbons with a small amount of sulphur.

In the presence of oxygen the conversion takes place at a somewhat lowertemperature than in the absence of this gas. Further-more the combustionof the divalent sulphur compounds to form sulphur furnishes heat whichis consumed by the dehydrogenation of the hydrocarbons. This latteradvantage is also involved if oxyg n is added in the case of the directinteraction of II ,nbsorbing the resulting hydrogen sulphide acondennteamoimtingtoimm'loto'lfipercentoitbeinltialgaslsobtainedbycoolingthegas to60belowleroC. Thesaidcondensatecontainsmpercentolbutyleneandmpercentofbutanewhichcorrespmdstoayieldoifljper centoi' butylene with reference tothe initial butane.l1theresldualbutanea1terseparation oftge butyleneissubjeet'edoncemore'tothe sam treatmentatotalyieldoido percent ofbublene is obtained.

The hydrogen sulphide formed from the sulphur may be removed from thereaction gases by absorption, for example with organic bases or withpotash solution, and then, after expelling it therefrom, it may be addedto further charges of saturated hydrocarbons to be converted. Thehydrogen sulphide may also be worked up to sulphur in the Claus furnace,the resulting sulphur being employed again for the conversion accordingto the present invention.

The following examples will further illustrate the nature of theinvention, but the invention is not restricted to the particularoperations described in these examples.

Example 1 60 liters of butane are passed per hour at about 340 C.through molten sulphur, a mixture of 1 molecular proportion of butaneand 1.2

atomic proportions of vaporized sulphur thus being obtained. Thismixture is passed at 625 C. over 0.1 liter of pumice, whereupon thetreated gas is cooled to 120? C. in order to condense the sulphur notconverted into hydrogen sulphide. (This sulphur may be used for reactingwith further amounts of saturated hydrocarbons.) The gas is then cooledto ordinary temperature and washed with a solution of triethanolamine inorder to remove the hydrogen sulphide. The purified gas is thereuponcompressed to l0.atmospheres and cooled to about 0., whereby a mixtureconsisting of about 40 per cent of butane and 60 per cent ofbutylene iscondensed together with small amounts of low boiling liquidhydrocarbons. The butylene is separated from the condensate by washingwith a 60 per cent sulphuric acid and then recovered from the sulphuricacid solution, while the butane is returned to the heat-treatment asdescribed above.

The uncondensed gas amounts to about 2.75 liters per liters of initialgas; it contains be- The hydrogen sulphide expelled from the solution oftriethanolamine is burnt in a Claus iurnace with the formation ofsulphur, which may be used for the conversion of further amounts ofbutane. I

' Example 2 60 liters of a mixture of butane and propane are passed perhour at about 550 C. over pyrite. The resulting mixture of hydrocarbonsand vaporous sulphur (one molecular proportion of hydrocarbon to eachatomic proportion of sulphur) is passed at about 600 C. over. 0.1 literof a mass free from iron prepared by impregnating 500 parts of coke witha solution of parts oi. tartar emetic and drying.

The resulting gas is further treated similarly as described inExample 1. The gas freed from hydrogen sulphide is cooled down to belowzero C. instead of 0 0., whereby propane, butane and the correspondingunsaturated hydrocarbons are condensed from the gas. The condensed gasamounts to 92 per cent of the initial gas; it con- Example 3 A mixtureof liters of butane, 20 liters of hydrogen sulphide and 150 liters ofair is passed at about 400 C. over 0.1 liter of silica gel. Theresulting gas ispurified from hydrogen sulphide as described inExample 1. By cooling to low temperatures per cent of the initial gas isrecovered unconverted. The condensed gas consists of 72 per cent ofoleflns. The uncondensed gas contains 28 per cent of oleflns.

What I claim is:

1. A process for the production of oleilns which comprises reacting at atemperature between 400" and 700 C. a paraflinic hydrocarbon containingfrom 3 to 6 carbon atoms in the molecule with sulphur iniermediarilyformed by the interaction at the said temperature 0! oxygen on a sulphurcompound capable oi reacting with oxygen with the formation of sulphur,and in an amount to cause a substantial conversion of said hydrocarboninto hydrogen sulphide and an olefin having the same number of carbonatoms as the said parafllnic hydrocarbon.

2. A process as claimed in claim 1 in which the divalent sulphurcompound is hydrogen sulphide.

, HANS BAEHR.

